6. The central role in membrane biosynthesis is played by:

Answer: (C) endoplasmic reticulum

2. Restriction endonucleases which recognize and cut at the same site of recognition sequences are known as:

Answer: (A) Isoschizomers

• Isoschizomers are restriction enzymes that recognize the same DNA sequence and cleave the DNA at the same positions within that sequence.

3. Which one of the following features is a mismatch repair?

Answer: (C) Parent and daughter strands of newly replicated DNA are distinguished

• Mismatch repair is a DNA repair mechanism that corrects errors made during DNA replication. It involves distinguishing between the newly synthesized strand and the template strand, and then repairing the mismatched base on the newly synthesized strand.

4. Exon skipping is associated with:

Answer: (D) RNA processing mutation

• Exon skipping is a type of RNA processing mutation that results in the exclusion of one or more exons from the mature mRNA. This can lead to the production of a truncated or non-functional protein.

5. A segment of DNA has 30 adenine and 30 cytosine bases. The total number of nucleotides present in this segment is:

Answer: (C) 60

• DNA is double-stranded, so each strand contains 30 adenine and 30 cytosine bases. Therefore, the total number of nucleotides is 30 (A) + 30 (C) + 30 (T) + 30 (G) = 120.

6. A transcription unit is 8000 nucleotide long. If only 15% of this unit codes for protein, calculate the approximate molecular weight of the protein encoded.  

Answer: (A) 44kDa

• 15% of 8000 nucleotides = 1200 nucleotides
• Each amino acid is encoded by 3 nucleotides, so 1200 nucleotides code for 400 amino acids.
• The average molecular weight of an amino acid is 110 Da, so the approximate molecular weight of the protein is 400 * 110 = 44,000 Da or 44 kDa.

7. A purified dimer protein of 70kDa when ran on SDS-PAGE, give single band. What would be the size of the band?

Answer: (B) 35kDa

• SDS-PAGE separates proteins based on their molecular weight. When a dimer protein is treated with SDS, it dissociates into its individual subunits. Therefore, the band on the SDS-PAGE gel will correspond to the molecular weight of a single subunit, which is 70 kDa / 2 = 35 kDa.